This invention relates to an operation mode controller which is utilized in controlling a temperature level in a refrigerating room by use of a refrigerator or the like equipped with, e.g., a thermostat.
FIG. 1 shows a basic function of a thermostat incorporated in a conventional temperature control apparatus such as a refrigerator or the like used for, e.g., marine transportation.
The thermostat outputs an "H" level when a measured temperature exceeds T.sub.H during a rise in temperature, and an "L" level when the temperature is lowered less than T.sub.L. When the indoor temperature of the refrigerating room rises and exceeds T.sub.H, an output level of the thermostat becomes "H" to start refrigerating operation. On the other hand, when the indoor temperature is lowered to T.sub.L, the thermostat output becomes an "L" level to stop the refrigerating operation.
FIG. 2 illustrates the operation of two thermostats connected in series.
An output level of the paired thermostats can assume three output levels "I", "II" and "III". More specifically, when the temperature sensed by the thermostats falls below T.sub.2 from the state where the sensed temperature was high and an output level was "I", the output level becomes "II". When the sensed temperature is further lowered, below T.sub.1, the output level now becomes "III". On the other hand, when the indoor temperature rises while in the state of output level "II" and the sensed temperature exceeds T.sub.4, the output level returns to "I". Similarly, when the indoor temperature rises while in the state of output level "III" and the sensed temperature exceeds T.sub.3, the output level returns to "II".
FIG. 3 shows operations of the individual thermostats A and B as the complex thermostat of FIG. 2.
The complex thermostat of FIG. 2 produces three output levels: "I" when both thermostats A and B are at an "H" level, the output level "II" when the thermostat A is at "L" and the thermostat B is at "H"; and the output level "III" when both thermostat A and B are at the output level "L".
When the temperature control apparatus incorporating such a complex thermostat is of, e.g., a heating-cooling system, the output level "I" of the thermostat corresponds to the state of cooling operation, the output level "II" corresponds to the state of operation shutdown, and the output level "III" corresponds to the state of heating operation.
In this case, now assuming that the difference between the temperature near an air blow-off port and temperature T.sub.2 in the heating-cooling system is T.sub.C at the beginning of cooling operation and the difference between the temperature near the air blow-off port and temperature T.sub.3 is T.sub.H at the beginning of heating operation .DELTA., T.sub.1 of the thermostat B in FIG. 3 and T.sub.4 of the thermostat A must be preset so that the difference between T.sub.2 and T.sub.4 is larger than .DELTA.T.sub.C and the difference between T.sub.1 and T.sub.3 is larger than .DELTA.T.sub.H, respectively, to prevent the immediate return to the former level due to a large temperature difference at the beginning of cooling and heating operation. Further, T.sub.1 must be preset lower than T.sub.2 and T.sub.4 must be set higher than T.sub.3 in order to prevent direct switching of operation modes from heating to cooling or vice versa.
Control limit temperature T.sub.0 of the air conditioner equipped with the foregoing complex thermostat is in a range from heating start temperature T.sub.1 to cooling start temperature T.sub.4. In this way, a width of the control temperature must be preset larger than temperature differences .DELTA.T.sub.C and .DELTA.T.sub.H. This is very disadvantageous for high-accuracy temperature control.
The present invention resolves the problem as mentioned above. It is an object of the present invention to provide an operation mode controller which permits high-accuracy temperature control by restricting a control temperature width of the thermostat as small as possible and is applicable in controlling, e.g., the refrigerating state of a refrigerator used for marine transportation.